Technical Field
The present invention relates to a sputtering tube target used for coating a substrate of a photovoltaic element, and in particular, to a method for preparing an ultra-long-tube type fine-grain molybdenum tube target made of pure molybdenum powder.
Related Art
Currently, sputtering tube targets at home and abroad for coating a substrate of a photovoltaic element are mainly made of a tungsten material, where the product specifications thereof are all small tube targets, the lengths are all less than 1700 mm, and the wall thicknesses are all greater than 40 mm. The compactness of a tungsten spin-coated sputtering tube target is relatively small during a sputtering coating process. Therefore, when bombardment is performed on a sputtering target, air in pores inside the target is released suddenly, causing the spattering of large-sized target particles or microparticles, or when secondary electron bombardment is performed on a film after the film is formed, the spattering of microparticles is caused. In addition, during the sputtering, target atoms would be easily preferentially sputtered out along the most compact arrangement direction of six directions of the atoms. Defects of physical properties of the material of a tungsten product directly affect a service performance of a coated film.
In order to change and overcome the defects and realize the maximum sputtering rate, a general practice is changing crystal structures of a target to increase the sputtering rate. In order to reduce air pores in a solid target and improve performances of a film, some practices adopt increasing the thickness of the target to improve the quality of the coated film.
At abroad, in order to improve the quality and effect of a tube target in coating a substrate of a photovoltaic element, a molding process of extruding or drawing is usually adopted. In order to overcome defects of the extruding or drawing process, an over-sintering process and a forging molding process are adopted, including steps of: high-temperature sintering-decreasing the temperature-increasing the temperature again and then forging-low-temperature annealing-fine processing. For example, in the technical solution of CN patent application 201110242640X, when molding is performed on a tungsten material, after high-temperature sintering, a water circulation temperature decreasing treatment needs to be adopted. Moreover, for example, in two technical solutions of CN patent application 2012100007317 and CN patent application 201210000729X, when a molybdenum material is processed, both of the two technical solutions adopt a process that needs a water circulation temperature decreasing treatment after high-temperature sintering. Although the processing methods of the process are helpful in increasing the compactness of a material, the processing methods of the process cannot form fine-grain structures.
Besides, there is another substantial defect in the prior art, that is, during a forging process, directly forging the surface of a tube blank is adopted, and the deformation amount of the material during the forging is uncontrollable. Therefore, the forging method substantially affects the formation and quality of fine-grain structures.
Moreover, in the prior art, the temperatures for annealing all adopt low temperatures, and the temperatures for annealing are all in the range of 450-500° C. The temperature for annealing is too low, and therefore, the formation of fine-grain structures of a product is substantially destroyed and the quality of the product is affected.
The processes of the prior art are complex, which causes relatively poor quality, increased cost, poor tube target compactness, and large grain size. As a result, when a film is coated, the uniformity and the layout quality of the film are substantially reduced, thereby failing to meet impedance ratio and film stress requirements of a material for a solar photovoltaic product.